1. Field of the Invention
The present invention relates generally to the field of apparatus for coating a conduit surface. More specifically, the present invention discloses an apparatus to accurately elevate a coating device to coat the inner surface of a conduit.
2. Statement of the Problem
Conduits are often used to carry fluids or abrasive slurries as part of a treatment or disposal process. As the fluid passes through the conduit, frictional forces against the conduit walls can cause the conduit walls to wear. The effect of these frictional forces is magnified on the curved portions of the conduit as a result of complex flow patterns and the forces from the fluid impacting the conduit surface caused by the fluid changing direction. Abrasives suspended within the fluid (e.g., solids commonly associated with mining slurries or sludge) can be even more detrimental to the conduit walls. Whatever the cause, these forces cause the conduit walls to wear even faster, eventually causing the conduit walls to crack or burst where the walls have worn thin.
To minimize the effects of these frictional forces on the conduit walls, a protective coating is applied (e.g., welded or sprayed) to the inner surface of the conduit. To provide effective protection against wear on the conduit wall, it is important that the entire area is completely coated with the coating material. Areas left unprotected will continue to be vulnerable to fracture.
An example of the prior art in this field is disclosed in U.S. Pat. No. 4,513,443 (Kostecki). Kostecki discloses an apparatus for coating an internal wall of a curved conduit with a layer of protective material. The apparatus has a guide means, a longitudinally flexible member, means for mounting a coating means for incremental rotation by the longitudinally flexible member, a drive means to drive the longitudinally flexible member relative to the curved conduit, and a means to automatically step the flexible member and consequently rotate the coating means. However, a disadvantage of using the flexible member in Kostecki is the associated inaccuracy in translating the rotational steps along the longitudinally flexible member. Because the coating means cannot be accurately rotated, the protective material can be misapplied resulting in either gaps or overlap between the applied strips of protective material.
A need exists to provide an apparatus to coat the internal walls of a conduit without sacrificing accuracy. In other words, conventional coating apparatus use a drive means remotely located from the coating device to elevate the coating device. As a result, error is introduced as the elevation drive is longitudinally translated from the remote position of the drive means. Consequently, portions of the conduit wall may be left unprotected. Alternately, in an attempt to eliminate unprotected surfaces, the spray pattern is severely overlapped, thus wasting the coating material.
3. Solution to the Problem
None of the prior art references uncovered in the search show an apparatus to coat a surface of a conduit having a center rod that provides for longitudinal movement of an index motor having a fixed rotational orientation relative to the center rod and positioned near a coating device so that the coating device is elevated directly proportionate to the index motor step to accurately coat the conduit wall. Therefore, the elevation of the coating device must be precisely controlled so that gaps are not formed between the strips of protective layer and to eliminate wasted coating material caused by overcorrecting, both potentially introduced by conventional coating apparatus.